I find the main difference is in the way I set up my prompt copy. I usually call from a self made composite of straight lines, vocal score and orchestral score, and that when calling, I tend to use a stop watch more.
The Orchestra (calling them a band will often get you lynched) are usually fairly independent from the rest of the show, which is a blessing and a curse.
I find the calling of the show changes depending on the MD and orchestral setup. Some MD's like to be cued before certain numbers (I don't know many, but I find that in orchestras which are cut down (say 5/10 people plus a whole heap of midi devices or pre-recorded stuff) a couple of MD's like a standby so that they can cue up the equipment). Some MD's want nothing to do with the stage manager, other than to receive a "Go" for the Overtures.
At your level, with a school band/orchestra, you may need to talk to the MD about making sure the band knows proper procedure for tuning and behavior etc. It is an ongoing debate in a number of SM circles, but I am firmly of the belief that no unnecessary sounds should come out of the bands instruments whilst the house is open. That means tuning is fine. It does however mean that a trumpet player should not be playing the star wars theme, whilst a clarinetist practices his/her C-minor arpegios, whilst a bass guitarist plays the mission impossible theme.
High school bands are notoriously unprofessional - I know because I was in one for my entire time at high school, and that involved going to various eisteddfod's, visiting other schools, and touring. Prior to my high school band career, I was in a choir. Choirs, as a general rule, are anally retentive about professionalism when entering/exiting/standing in front of an audience. Most high school bands are shockers. In the corridor outside the hall, trumpets blasting notes, trombones pretending to be race cars etc - all of which can be heard by the front rows. Put them in an orchestra pit, where they believe they are next to invisible, in an auditorium designed acoustically, so that an un-miced voice talking at a reasonable volume can be heard and you are in trouble.
I suppose the moral is to talk to the MD and make sure (since you are a student and I assume the MD is a music teacher of some description) that your concerns re: behavior whilst the house is open are understood, and that the message is passed on and enforced.
Also - find out what form of communication you will have between yourself and MD. Some MD's refuse to use cans (even before show) and all you will have to work with is a cue light. It is hard to convey messages through cue lights, unless you are both proficient at Morse code, so if that is the case, and if at all possible, it may be worth having an ASM in blacks able to act as a runner (if the pit is raised to performance height whilst the house is open) or an ASM at the pit doors if the pit will remain lowered until show start.
The core duties of a stage manager remain basically the same - look after everyone, make sure things happen on time, and enjoy it... Just don't start singing along, because people on cans will look at you funny afterwards... and there is a chance that you might be heard.